Method of purifying and concentrating lithium ions

ABSTRACT

1. A METHOD OF PURIFYING AND CONCENTRATING LITHIUM IONS FROM AN AQUEOUS SOLUTION WHEREIN THEY ARE CONTAINED TOGETHER WITH OTHER IONS WHICH METHOD COMPRISES ADDING TO SAID SOLUTION A CAUSTIC SOLUTION TO OBTAIN A SOLUTION WHEREIN THE CONCENTRATION OF HYDROXYL IONS IS EQUAL AT LEAST TO THE LITHIUM ION CONCENTRATION; PERCOLATING THE SOLUTION SO OBTAINED THROUGH A BED CONSISTING OF CRYSTALLINE THORIUM ACID ARSENATE HAVING THE FORMULA TH(HASO4)2 AND AN ION EXCHANGE CAPACITY RANGING BETWEEN 1.40 ND 3.55 ME./G. TOWARD THE LITHIUM ION TO THEREBY OBTAIN THORIUM AND LITHIUM ARSENATE; WASHING SAID THORIUM AND LITHIUM ARSENATE WITH WATER PREVVIOUSLY ALKALIZED AT A PH FROM 9 TO 10; PERCOLATING A HYDROCHLORIC ACID SOLUTION THROUGH SAID THORIUM AND LITHIUM ARSENATE TO ELUTE THE LITHIUM IONS THEREFRM WHEREBY A CONCENTRATED AND PURIFIED LITHIUM SOLUTION IS OBTAINED AND THE THORIUM ARSENATE IS RESTORED TO ITS INITIAL FORM.

United States Patent US. Cl. 423181 1 Claim ABSTRACT OF THE DISCLOSURE Amethod of purifying and concentrating lithium ions in an aqueoussolution comprises the steps of adding a base to a solution containinglithium ions to provide a concentration of OH ions in the solution whichis greater or equal to the lithium ion concentration. Thorium acidarsenate is added to the resultant solution, whereby thoriurn lithiumarsenate is formed. The arsenate is then washed in alkalinized water andlithium is removed from the arsenate with an acid solution, whereby theexchanger is restored to its original acid form and a purifiedconcentrated lithium solution is obtained. The thorium acid arsenate maybe a crystalline thorium acid arsenate having the formula Th(HAsO withan ion exchange capacity ranging between 1.40 to 3.55 meq./g. relativelyto the lithium ion.

This invention relates to a method of purifying and concentratinglithium ions in an aqueous solution.

This application is a continuation-in-part of our copending patentapplication Ser. No. 846,586, filed July 31, 1969' and now abandoned.

In accordance with the present invention thorium acid arsenate is usedfor purifying and concentrating lithium ions from their solutions.

Thorium arsenate is a comparatively recently produced inorganic ionexchanger which as compared to all other known exchangers, is the onlyone which can exchange lithium ions. The reason lies in its crystallinestructure which is particularly compact. Only lithium ions due to theirsmall size can penetrate into this structure and replace hydrogen ionsin the exchanger, While all other ions having a larger radius stayoutside and can be retained at the surface only.

Thus thorium arsenate acts as a very fine ionic sieve. The ion exchangeprocess is a reversible one and may be expressed as follows:

In an alkaline environment (pH 9.5) thorium arsenate is totallytransformed into a lithic form. In an acid environment thorium arsenatein lithic form is totally restored to original hydrogen form and lithiumconcentrates in the acid solution. In the following table some values ofthe exchanging ability of the thorium arsenate towards the lithium ionare shown at different pH values of the solution containing it. Thoriumarsenate is stable enough with respect to hydrolysis and it does notlose any significant amount of arsenate ions at pH 12.

TABLE Values of the ion exchange capacity of thorium arsenate toward thelithium ion at some pH vvalues of the solution "ice containing it (theinitial concentration of Li+ in the solution being equal to 0.1meq./ml.).

Li+ in the exchanger An object of the present is the provision of aneflecti've method of purifying and concentrating lithium ions by the useof thorium acid arsenate preferably prepared in accordance with methodsdescribed hereinafter.

Other objects will become apparent in the course of the followingspecification.

Thorium acid arsenate may be obtained from a solution containing arsenicacid and a thorium salt by boiling it for a sufiicient period of time orby placing it in an autoclave at temperatures higher than C. The bestresults are achieved with concentrations of arsenic acid in the range of2 to 4 M and with concentrations of a thorium salt in the range of 0.1to 1 M while the molar ratio of the aresnic acid to the thorium salt ismaintained in the range 2 to 20.

The following examples describe by way of illustration only preferredmethods of preparing thorium acid arsenate:

EXAMPLE 1 A 1-2 molar solution of thorium nitrate in nitric acid wasmixed with a solution of arsenic acid to obtain a solution of which thefinal molar concentrations were 0.33 thorium nitrate, 3.3 arsenic acidand 1.2 nitric acid. This solution was kept boiling to fall back until amicrocrystalline precipitate was formed which generally oc curred 2-5days after the boiling was started. The boiling to fall back was thencontinued until no significant modifications were observed in the X-raydiffraction spectrum of samples taken out at various stages of theboiling operation. The average boiling time to start the precipitationin the different tests was about 200 hours. The material was thenseparated from the solution, washed with distilled water to attain a pHvalue ranging between 4 and 5 and finally dried in air. The finalproduct was in the form of a white powder.

EXAMPLE 2 A solution identical to that prepared in Example 1 was placedin an autoclave at temperatures slightly higher than 100 C. (l03110 C.).After a period of time varying from 2 to 10 days depending on thetemperature the precipitated material was separated from the solution.The subsequent process steps were the same as in Example 1.

This process is speedier than that described in Example 1.

Thorium acid arsenate prepared in the above-described manner can be usedfor purifying and concentrating lithium salts according to the followingmethods:

EXAMPLE 3 The lithium salts solution to be processed is first alkalizedwith any base such as NaOH, KOH, Ca(OH) NH etc. In determining theamount of the base to be added it should be kept in mind that theconcentration of the OH- ions in the solution must at least equal theconcentration of the Li+ ions.

If any ions are also present in the solution which are capable offorming insoluble hydroxyls, a precipitate may separate from thesolution. In such case the precipitate should be removed from thesolution. The alkaline solution is then slowly percolated through achromatographic column containing the thorium acid arsenate. In this waylithium is separated from the other ions in the solution because lithiumonly is retained by the exchanger. A small volume of distilled water isthen percolated which had previously been alkalized to pH 9-10 with NaOHfor the purpose of washing the thorium arsenate in lithic form off theadhering solution. Subsequently, a small volume of acid solution ispercolated for the purpose of eluting the lithium ion from theexchanger. In this way the thorium arsenate is restored to its originalhydrogen form while the lithium ion is purified and concentrated in asmall volume of solution. In order to use again the thorium acidarsenate in a fresh cycle, it suffices to wash it in the column withdistilled water.

It is apparent that other procedures may be used for converting thoriumacid arsenate into its lithic form and for restoring it into itshydrogen form. For example, currently used industrial processes of ionexchange can be applied, such as a mobile bed of exchanger or a processin countercurrent.

It is also possible to add thorium acid arsenate directly to the processsolution containing lithium ions, thorium arsenate being subsequentlyrecovered through filtration or centrifuging.

The following example sets forth by way of illustration only, a methodof purifying and concentrating lithium from a lithic solution containingsodium:

EXAMPLE 4 To one liter solution containing 110 mg. lithium and 2,300 mg.sodium, 5 g. thorium arsenate and 0.8 g. NaOH were added. After a threeday contact with the solution the exchanger was removed from thesolution by filtration or centrifuging. In such conditions an amount ofthe lithium in the solution greater than 90% was retained by theexchanger. The lithium ion was eluted from the exchanger with 50 ml.hydrochloric acid 0.4 N. The chemical analysis of the elution gave thefollowing quantities as an average of various tests: lithium: 101 rn-g.;sodium: 2 mg. Thus, with the process as above described the twofoldobject was achieved of purifying the lithium ion from strongconcentrations of sodium and substantially concentrating it. In additionthe exchanger is totally restored to its original hydrogen form readyfor being used again in further process cycles.

It is apparent that various changes can be made in the describedexamples within the scope of the appended claim.

What is claimed is:

1. A method of purifying and concentrating lithium ions from an aqueoussolution wherein they are contained together with other ions whichmethod comprises adding to said solution a caustic solution to obtain asolution wherein the concentration of hydroxyl ions is equal at least tothe lithium ion concentration; percolating the solution so obtainedthrough a bed consisting of crystalline thorium acid arsenate having theformula Th(HAsO and an ion exchange capacity ranging between 1.40 and3.55 meq./g. toward the lithium ion to thereby obtain thorium andlithium arsenate; washing said thorium and lithium arsenate with waterpreviously alkalized at a pH from 9 to 10; percolating a hydrochloricacid solution through said thorium and lithium arsenate to clute thelithium ions therefrom whereby a concentrated and purified lithiumsolution is obtained and the thorium arsenate is restored to its initialform.

References Cited OTHER REFERENCES LeFlem et al.: Le systme As O -Th0Bulletin de la Socit Chemique de France, fascicule 6, June 1966, pp.1180-83.

CARL D. QUARFORTH, Primary Examiner R. L. TATE, Assistant Examiner US.Cl. X.R.

1. A METHOD OF PURIFYING AND CONCENTRATING LITHIUM IONS FROM AN AQUEOUSSOLUTION WHEREIN THEY ARE CONTAINED TOGETHER WITH OTHER IONS WHICHMETHOD COMPRISES ADDING TO SAID SOLUTION A CAUSTIC SOLUTION TO OBTAIN ASOLUTION WHEREIN THE CONCENTRATION OF HYDROXYL IONS IS EQUAL AT LEAST TOTHE LITHIUM ION CONCENTRATION; PERCOLATING THE SOLUTION SO OBTAINEDTHROUGH A BED CONSISTING OF CRYSTALLINE THORIUM ACID ARSENATE HAVING THEFORMULA TH(HASO4)2 AND AN ION EXCHANGE CAPACITY RANGING BETWEEN 1.40 ND3.55 ME./G. TOWARD THE LITHIUM ION TO THEREBY OBTAIN THORIUM AND LITHIUMARSENATE; WASHING SAID THORIUM AND LITHIUM ARSENATE WITH WATERPREVVIOUSLY ALKALIZED AT A PH FROM 9 TO 10; PERCOLATING A HYDROCHLORICACID SOLUTION THROUGH SAID THORIUM AND LITHIUM ARSENATE TO ELUTE THELITHIUM IONS THEREFRM WHEREBY A CONCENTRATED AND PURIFIED LITHIUMSOLUTION IS OBTAINED AND THE THORIUM ARSENATE IS RESTORED TO ITS INITIALFORM.